The present invention relates to an internal combustion engine having one or more reciprocating valves. It is common to provide springs for urging such valves to the closed position and to provide a cam mechanism for opening the valves. The disadvantages of these known arrangements are well known.
There have been proposed alternative arrangements for operating reciprocating valves which do not rely upon biasing of the valves by means of springs. An example of such a proposal is disclosed in an article in the Journal "Motor Cycle" issued 1st May 1958. This article describes an arrangement proposed by one R. Gardner and is referred to herein as the "Gardner arrangement". In the Gardner arrangement, there is provided for each valve a rocker mounted adjacent to one of its ends for rocking about a fixed pivot axis and connected adjacent to its opposite end with a stem of the valve. An intermediate portion of the rocker is of annular form and defines an internal cam track. The cam track is engaged at diammetrically opposite positions by two rollers which are moved around a circular path, centered on an axis of a camshaft. The cam track is non-circular so that the rocker is caused to rock about its pivot axis as the rollers move around the camshaft axis.
A relatively large space must be provided in the engine to accommodate the rockers of the Gardner arrangement. This limits the choice in the disposition of other parts of the engine, for example in the routing of inlet ducts and exhaust ducts. Each rocker inevitably possesses considerable mass and so quite large forces have to be exerted to overcome the inertia of the rocker. A further disadvantage of the Gardner arrangement is that the motion of the rocker relative to the camshaft axis is along an arcuate path centered on the pivot axis. The rocker executes angular motion relative to the corresponding valve.